1. Field of the Invention
The invention relates generally to a wrench and fastener arrangement and more particularly to a wrench and fastener arrangement with driving surfaces that generate a higher torque in the loosening direction than in the tightening direction or higher torque in the tightening direction than in the loosening direction.
2. Description of the Prior Art
Wrenches and fasteners have been known in the art for some time. Current wrenches and the mating surfaces of fasteners have been designed symmetrically and have the property of transmitting torque equally in both the tightening and loosening directions. Typical socket wrench types of this kind are shown in FIGS. 1-3. FIG. 1 shows a 1 xc2xdxe2x80x3 Hex socket, FIG. 2 shows a 1xe2x80x312 point socket, and FIG. 3 shows a 1xe2x80x312 point spline. However, the torque required for loosening a fastener that has been tightened is several times more than the torque required for tightening a fastener. This is because metal surfaces in contact with one another for an extended period of time tend to seize and resist separation. Another factor that causes the fastener to resist separation is the dissolution of the lubricant that may have been present at the time of tightening. Additionally, tightening of a fastener to near its ultimate strength will cause permanent deformation. This permanent deformation causes the pitch of the threads on the fastener to no longer precisely match the pitch of the nut or the tapped hole. The mismatch requires additional torque to force the threaded elements to conform sufficiently to allow rotation of the fastener. Additionally, fastener heads are typically forged. High strength fasteners are typically made from material that is difficult to forge. This material tends not to fill out the outer corners of the fastener, or the inner corners of wrenches.
Other fastening arrangements require using fasteners that will never be removed for security reasons. Systems currently in use include fasteners having two heads where the top head is twisted off during tightening. However, these systems do not have the high torque capability of the present invention.
In accordance with a preferred embodiment of the present invention, a high torque wrenching system is provided having a wrench with asymmetrical torque transmission capability. The system further provides a fastener that can mate with the asymmetrical wrench so that the fastener can be axially rotated to a loosened or tightened state. The wrench can be a socket type, an open end type, a closed end type wrench or an internal wrench type. The wrench includes a plurality of protuberances and a plurality of recesses around a central axis. The protuberances and recesses form a saw tooth shape. Each tooth or protuberance is formed by a first wrenching surface for loosening a fastener and a second wrenching surface for tightening a fastener. The wrenching surface carrying the loosening load will be at a much smaller angle, with respect to a radial vector extending from the wrench""s central axis, than the wrenching surface carrying the tightening load. The result is that the loosening torque vector will have a much greater moment arm. Further, the mating relationship will be less sensitive to dimensional variations of the fastener and wrench, because a better distribution of load can be accomplished on the loosening surface than on the tightening surface, even though the tightening surface is much larger. The load transmission increases proportionally to the number of protuberances or teeth. Therefore, the number of teeth can vary depending on the application or particular torque requirements. Additionally, more teeth will allow the use of a smaller head diameter for a given fastener""s size because the difference between the major and minor diameters is less.
The invention also provides a fastener that is easier to forge because the outer connecting surface of the protuberances is smaller in cross-sectional area than the inner connecting surface of the recesses. This tends to squeeze the metal to the corners during forging Additionally, the greater slope on the loosening surface than on the tightening surface tends to move the metal toward the tightening surface, filling the right-hand corner of the outer connecting surface of the fastener and the left-hand corner of the outer connecting surface of the wrench. These are on the portions of the wrench that carry the loosening load, which is the greater load. Therefore, it is desirable to have only a small radius in the corner to make the load carrying surface as large as possible.
An example of a mating fastener type could be a typical hexagonal head with a cross flats dimension of approximately one and a half times the bolt diameter. For the same bolt diameter, a 12-point fastener version with a cross flats of one times the diameter could be provided. Standard 12-point fasteners depending on the details of their construction, including head height and material hardness, may not have sufficient wrenchability to fully utilize the properties of the fastener. Using asymmetrical surfaces increases the torque ability while still preserving the small 12-point heads. Additionally, 15-point variations could increase torque requirements while allowing smaller heads. The wrenching surfaces may be straight or have some curvature or tilt. In particular, it could be beneficial for the tightening surface to have some curvature or tilt to help control and improve the contact pattern despite variations in fastener and wrench dimensions.
The fastener also includes a plurality of protuberances and a plurality of recesses. The protuberances of the wrench mate with the recesses of the fastener, and the protuberances of the fastener mate with the recesses of the wrench. This arrangement is beneficial because it precludes the use of common wrench and fastener types outside this system, which could result in the risk of injury because of failure of lesser strength tool types. The fastener and wrench could be comprised of a special material and hardness, such as a pressed-on ring, to further increase its ability to transmit a higher torque than a standard socket.
According to an aspect of the preferred embodiment of the invention, a wrenching system is provided wherein the wrenching surface carrying the tightening load is at a much smaller angle, with respect to a radial vector extending from the wrench""s central axis, than the wrenching surface carrying the loosening load. The result is that the tightening torque vector will have a much greater moment arm. This aspect provides for fasteners that cannot be removed. Preferably, the wrench and fastener tightening surfaces are nearly radial. The loosening surface would be at a greater angle than as previously discussed above for a high torque loosening system because the loosening surface would not be used for transmitting torque, but rather would be provided for backside support and support for the torque transmitting surfaces.
Ridges or other projections may be added to the tightening surface of the fasteners, such that the fasteners would be deformed when sufficient load is applied during the process to prohibit removal of the fastener. For large size fasteners, proper deformation of the fasteners can be verified by inspection. For smaller fasteners, a gage can be made that only fits on the fastener when the projections have been properly deformed.
In yet another aspect of the invention, a two headed fastener is provided having an upper head connected to a lower head by a neck portion. The upper head is a twist off head that breaks away from the fastener when a predetermined torque is reached. The upper head has a diameter that is as small or preferably smaller than the diameter of the lower head. The upper head has a tightening surface that is at a much smaller angle than the loosening surface. The lower head has preferably a nearly rounded surface so that once the fastener is tightened and the upper head twisted off when the appropriate torque is reached, the lower head cannot be loosened and removed.
An object of the present invention is to provide a high torque wrenching system.
Another object of the invention is to provide a wrenching system that transmits more torque when loosening a fastener than when tightening a fastener.
Another object of the present invention is to provide a high torque wrenching system that can be used on heads having larger and smaller diameters.
A further object of the present invention is to provide a wrenching system that transmits higher torque with minimum sized fasteners and wrenches.
Another object of the invention is to provide a high torque wrenching system that cannot mate with members outside the system having lesser strength tools that may result in the risk of injury.
Another object is to provide high strength fasteners that are easier to forge than conventional high strength fasteners.
Another object of the invention is to provide a wrenching system that transmits more torque when tightening a fastener than when loosening a fastener.
Yet another object of the invention is to provide a wrenching system with a fastener that cannot be loosened and removed.
A further object of the invention is to provide a high torque two headed twist off fastener.